Abstract
Optical model analyses of recent elastic scattering data for incident energies of 16 and 22 MeV, together with existing data for at the same energies, reveal a significant difference in the behavior of the imaginary part of the optical potential for the two isotopes as the incident energy is reduced below the Coulomb barrier. While the strength of the imaginary potential reduces as the incident energy is reduced below the barrier, as is the case for most heavy ions, that for remains constant within uncertainties and may even increase. Similar behavior was observed for the and optical potentials [Nucl. Phys. A 571, 326 (1994)], with the strength of the imaginary potential appearing to increase as the incident energy is reduced below the Coulomb barrier while that for reduces. However, the explanation for this difference in behavior put forward in that work, viz. the increased importance of breakup for as the incident energy is reduced towards the Coulomb barrier, later supported explicitly by calculations [Phys. Lett. B 427, 1 (1998)], does not hold for the He isotopes since it is the optical potential that behaves in a similar fashion to that of in spite of having the higher breakup threshold of the two He isotopes. We conclude that the difference is due to the influence of and stripping on the scattering, reactions which cannot take place for projectiles.
- Received 1 October 2018
- Revised 18 December 2018
DOI:https://doi.org/10.1103/PhysRevC.99.024603
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